1. Field of the Invention
The invention relates to a method for producing rotational-symmetrical articles of sheet metal with double curved surface and varying thickness, particularly conical or bell-shaped articles such as rocket nozzles, in which a number of sheet metal part-blanks in flat condition are cut to partially circular ring-like shape, whereupon said sheet metal part-blanks thus cut are bent to the desired curvature about the intended axis of symmetry and welded together to form a blank of the article for final machining.
2. Descriptionn of the Related Art
The purpose of a rocket nozzle is to expand and accelerate a flow of gas to high velocity and thereby provide a propulsion thrust on the rocket.
The rocket nozzles must also be cooled, which can be done in either of three ways, viz. by regenerative cooling, radiation cooling or by covering the hot side of the nozzle wall with heat protective material. In the case of radiation-cooled nozzles the wall is a single layer structure. Such radiation-cooled nozzles or nozzles provided with heat protective material with conical or bell-shape and varying thickness of material have hitherto been produced by cutting a number of subpieces in flat condition from a plate with a thickness of material of for instance 4 mm, which are then bent to the desired curvature in respect of the axis of symmetry of the intended article, which subpieces are then put together to a closed ring shape and, if necessary, subjected to a shaping operation to obtain the double-curved form. Several similar ring bodies with different thickness of material are produced and finally put together in the longitudinal direction of the article in a predetermined sequence.
This method of manufacturing rocket nozzles suffers from a number of problems. Thus, the initial cutting of the subpieces requires very great accuracy for obtaining a perfect fit at the places of the joint. Joining of the different ring bodies to each other requires complicated tooling and control equipment adapted individually to each size of the ring bodies and the nozzles.
In many cases such nozzles are to be shaped with decreasing thickness of material from the smallest to the greatest cross section in order not to give the nozzle greater strength and thereby weight than what is required to withstand the pressures existing inside and outside the nozzle and other stresses. To obtain this the subpieces or the ring bodies are subjected to machining, preferably chip removal to obtain a progressive change in the thickness of material. This is time-consuming and costly.